The hollow-pointed stainless steel needle in combination with syringes and infusion pumps is the common tool used in the healing arts to invade the body when giving injections or withdrawing body fluids. The sharply pointed end of a needle is extremely dangerous, and accidental pricking is very common even among nurses and other trained personnel. If accidental pricking occurs after the needle has been extracted from a patient with contaminated body fluid, the patient's disease may be transmitted to the treating physician or nurse. Procedures have been established for the recapping and safe disposal of medical needles immediately after their use. But the recapping process itself can be hazardous especially when occurring in the traumatic surroundings of a first aid treatment at the site of an accident or in the context of an emergency room intervention. Various automatic recapping systems have been devised in the past of which a typical example is disclosed in U.S. Pat. No. 4,850,996 Cree. In such case a retractable rigid tube surrounding the needle is biased by a coil spring which is collapsed when the tip of the sheath is brought into contact with the skin of the patient. The needle moves axially within the sheaths until it emerges at the distal end to penetrate the patient's tissue. This type of protective device is relatively complex and expensive to manufacture due to its multitude of components. It also does not provide a safe and automatic locking of the needle within the protective sheaths after use. Accordingly, there is a need for a simple and more effective way to automatically shield the tip of a medical needle after it has been withdrawn from the body of a patient.